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Hydrogen assisted cracking of a subsea-flowline

  • Since the mid-nineties, supermartensitic stainless steels (SMSS) have increasingly been applied to welded subsea-pipeline systems in the North Sea oil and gas fields, especially to flowlines at mild sour service conditions. However, in 2001 cracking and leaks occurred during installation and service start-up of two SMSS flowlines in the Norwegian Tune gas condensate field, welded with a new developed matching filler wire. Brittle transgranular cracking started especially at inter-run lack of fusion and propagated brittle, predominantly through the weld metal. The present paper provides a brief overview of the original failure case and respective sequence of events leading to complete replacement of the SMSS by carbon steel flowlines in 2002. Then, detailed investigations of a circumferential weld sample of the failed Tune flowline are highlighted, targeted at comparison of the failure appearance to previous investigations of this filler material type and to search for possibleSince the mid-nineties, supermartensitic stainless steels (SMSS) have increasingly been applied to welded subsea-pipeline systems in the North Sea oil and gas fields, especially to flowlines at mild sour service conditions. However, in 2001 cracking and leaks occurred during installation and service start-up of two SMSS flowlines in the Norwegian Tune gas condensate field, welded with a new developed matching filler wire. Brittle transgranular cracking started especially at inter-run lack of fusion and propagated brittle, predominantly through the weld metal. The present paper provides a brief overview of the original failure case and respective sequence of events leading to complete replacement of the SMSS by carbon steel flowlines in 2002. Then, detailed investigations of a circumferential weld sample of the failed Tune flowline are highlighted, targeted at comparison of the failure appearance to previous investigations of this filler material type and to search for possible explanations for the brittle fracture at the crack initiation area. SEM investigations of the fracture surface revealed brittle areas only in the direction towards the top side of the weld while the major part of the investigated surface exhibited ductile fracture. As an approach to clarify, if the fracture was a consequence of hydrogen assisted cracking, five small sized specimens have been cut out of the original sample. Cracking has been introduced parallel to the original fracture surface in these specimens at respective saw cuts and bending. The results show that brittle transgranular cracking appeared only in the specimen cooled down to very low temperatures by liquid nitrogen and in the sample charged with hydrogen to an average concentration of about 15 ml/100 g. However, a fracture similar to the original surface was observed only in the hydrogenized specimen. As a further result, very similar fracture surfaces of supermartensitic stainless steel weld metals had been observed on specimens subjected to hydrogen assisted cold cracking (HACC) as well as to hydrogen assisted stress corrosion cracking (HASCC). In total, the results indicate that brittle fracture starting at the inter-run lack of fusion were not initiated by high notch tip deformation rates, but rather influenced by hydrogen, probably taken up during welding.zeige mehrzeige weniger

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Metadaten
Autoren/innen:Thomas Böllinghaus, Enrico Steppan, Tobias Mente
Persönliche Herausgeber/innen:Thomas Böllinghaus, J. C. Lippold, C. E. Cross
Dokumenttyp:Beitrag zu einem Sammelband
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Englisch):Cracking Phenomena in Welds IV
Auflage:1
Jahr der Erstveröffentlichung:2016
Organisationseinheit der BAM:9 Komponentensicherheit
9 Komponentensicherheit / 9.0 Abteilungsleitung und andere
Verlag:Springer International Publishing
Verlagsort:Switzerland
Erste Seite:Part V, 361
Letzte Seite:379
DDC-Klassifikation:Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Freie Schlagwörter:fracture topography; hydrogen assisted cracking; supermartensitic stainless steel
Themenfelder/Aktivitätsfelder der BAM:Material
Material / Degradation von Werkstoffen und Materialien
DOI:https://doi.org/10.1007/978-3-319-28434-7_17
URL:http://link.springer.com/chapter/10.1007/978-3-319-28434-7_17
URL:http://www.springer.com/us/book/9783319284323
ISBN:978-3-319-28432-3
ISBN:978-3-319-28434-7
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:29.03.2016
Referierte Publikation:Nein